Changing configuration structure to enable multiple accounts.

This change enables using multiple wire plugins at the same time.
Also, we now distinguish between the wire plugin (i.e. EBICS or
taler_bank) and the wire method (i.e. SEPA or x-taler-bank) that
the wire plugin is implementing.  The "taler-bank" wire method
was renamed from "test" to "x-taler-bank".

This also changes the format of the /wire response of the exchange,
as we now need to return multiple accounts.  Note that wire fees
are specified per wire method, not per wire account.

taler-exchange-keyup now automatically signs all of the /wire
responses in the location specified by the configuration.

Account identification in wire plugins was changed to use
payto://-URLs instead of method-specific JSON fields.  Signing
and validation of /wire responses was moved from each wire
plugin to a generic validation method in libtalerutil (crypto)
or libtalerjson (for JSON-formatted inputs).
Convenience methods were added to generate JSON for wire accounts
(salting, signing).

Various section and option names were adjusted to streamline the
configuration and make it more consistent overall.  Documentation
was updated as well.

1 files changed, 1284 insertions, 0 deletions

diff --git a/src/wire-plugins/plugin_wire_taler-bank.c b/src/wire-plugins/plugin_wire_taler-bank.c
new file mode 100644
index 000000000..2d2235343
--- /dev/null
+++ b/src/wire-plugins/plugin_wire_taler-bank.c
@@ -0,0 +1,1284 @@
+/*
+  This file is part of TALER
+  Copyright (C) 2017, 2018 Taler Systems SA
+
+  TALER is free software; you can redistribute it and/or modify it under the
+  terms of the GNU General Public License as published by the Free Software
+  Foundation; either version 3, or (at your option) any later version.
+
+  TALER is distributed in the hope that it will be useful, but WITHOUT ANY
+  WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
+  A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
+
+  You should have received a copy of the GNU General Public License along with
+  TALER; see the file COPYING.  If not, see <http://www.gnu.org/licenses/>
+*/
+
+/**
+ * @file plugin_wire_taler_bank.c
+ * @brief plugin for the "x-taler-bank" wire method
+ * @author Christian Grothoff
+ */
+#include "platform.h"
+#include "taler_wire_plugin.h"
+#include "taler_json_lib.h"
+#include "taler_bank_service.h"
+#include "taler_signatures.h"
+#include <gnunet/gnunet_curl_lib.h>
+
+/* only for HTTP status codes */
+#include <microhttpd.h>
+
+/**
+ * Maximum legal 'value' for an account number, based on IEEE double (for JavaScript compatibility).
+ */
+#define MAX_ACCOUNT_NO (1LLU << 52)
+
+/**
+ * Type of the "cls" argument given to each of the functions in
+ * our API.
+ */
+struct TalerBankClosure
+{
+
+  /**
+   * Which currency do we support?
+   */
+  char *currency;
+
+  /**
+   * Handle to the context for sending funds to the bank.
+   */
+  struct GNUNET_CURL_Context *ctx;
+
+  /**
+   * Scheduler context for running the @e ctx.
+   */
+  struct GNUNET_CURL_RescheduleContext *rc;
+
+  /**
+   * Configuration we use to lookup account information.
+   */
+  struct GNUNET_CONFIGURATION_Handle *cfg;
+
+};
+
+
+/**
+ * Handle returned by #taler_bank_prepare_wire_transfer.
+ */
+struct TALER_WIRE_PrepareHandle
+{
+
+  /**
+   * Task we use for async execution.
+   */
+  struct GNUNET_SCHEDULER_Task *task;
+
+  /**
+   * TalerBank closure we run in.
+   */
+  struct TalerBankClosure *tc;
+
+  /**
+   * Authentication information.
+   */
+  struct TALER_BANK_AuthenticationData auth;
+
+  /**
+   * Which account should be debited? Given as the respective
+   * section in the configuration file.
+   */
+  char *origin_account_url;
+
+  /**
+   * Which account should be credited?
+   */
+  char *destination_account_url;
+
+  /**
+   * Base URL to use for the exchange.
+   */
+  char *exchange_base_url;
+
+  /**
+   * Function to call with the serialized data.
+   */
+  TALER_WIRE_PrepareTransactionCallback ptc;
+
+  /**
+   * Closure for @e ptc.
+   */
+  void *ptc_cls;
+
+  /**
+   * Amount to transfer.
+   */
+  struct TALER_Amount amount;
+
+  /**
+   * Subject of the wire transfer.
+   */
+  struct TALER_WireTransferIdentifierRawP wtid;
+
+
+};
+
+
+/**
+ * Handle returned by #taler_bank_execute_wire_transfer.
+ */
+struct TALER_WIRE_ExecuteHandle
+{
+
+  /**
+   * Handle to the HTTP request to the bank.
+   */
+  struct TALER_BANK_AdminAddIncomingHandle *aaih;
+
+  /**
+   * Function to call with the result.
+   */
+  TALER_WIRE_ConfirmationCallback cc;
+
+  /**
+   * Closure for @e cc.
+   */
+  void *cc_cls;
+};
+
+
+/**
+ * Round amount DOWN to the amount that can be transferred via the wire
+ * method.  For example, Taler may support 0.000001 EUR as a unit of
+ * payment, but SEPA only supports 0.01 EUR.  This function would
+ * round 0.125 EUR to 0.12 EUR in this case.
+ *
+ * @param cls the @e cls of this struct with the plugin-specific state
+ * @param[in,out] amount amount to round down
+ * @return #GNUNET_OK on success, #GNUNET_NO if rounding was unnecessary,
+ *         #GNUNET_SYSERR if the amount or currency was invalid
+ */
+static int
+taler_bank_amount_round (void *cls,
+                         struct TALER_Amount *amount)
+{
+  struct TalerBankClosure *tc = cls;
+  uint32_t delta;
+
+  if (NULL == tc->currency)
+  {
+    GNUNET_log_config_missing (GNUNET_ERROR_TYPE_ERROR,
+                               "taler",
+                               "CURRENCY");
+    return GNUNET_SYSERR; /* not configured with currency */
+  }
+  if (0 != strcasecmp (amount->currency,
+                       tc->currency))
+  {
+    GNUNET_break (0);
+    return GNUNET_SYSERR;
+  }
+  /* 'taler_bank' method supports 1/100 of the unit currency, i.e. 0.01 CUR */
+  delta = amount->fraction % (TALER_AMOUNT_FRAC_BASE / 100);
+  if (0 == delta)
+    return GNUNET_NO;
+  amount->fraction -= delta;
+  return GNUNET_OK;
+}
+
+
+/**
+ * Information about an account extracted from a payto://-URL.
+ */
+struct Account
+{
+  /**
+   * Hostname of the bank (possibly including port).
+   */
+  char *hostname;
+
+  /**
+   * Bank account number.
+   */
+  unsigned long long no;
+};
+
+
+/**
+ * Parse payto:// account URL (only account information,
+ * wire subject and amount are ignored).
+ *
+ * @param account_url URL to parse
+ * @param account[out] set to information, can be NULL
+ * @return #TALER_EC_NONE if @a account_url is well-formed
+ */
+static enum TALER_ErrorCode
+parse_payto (const char *account_url,
+             struct Account *r_account)
+{
+  const char *hostname;
+  const char *account;
+  const char *q;
+  unsigned long long no;
+
+#define PREFIX "payto://x-taler-bank/"
+  if (0 != strncasecmp (account_url,
+                        PREFIX,
+                        strlen (PREFIX)))
+    return TALER_EC_PAYTO_WRONG_METHOD;
+  hostname = &account_url[strlen (PREFIX)];
+  if (NULL == (account = strchr (hostname,
+                                 (unsigned char) '/')))
+    return TALER_EC_PAYTO_MALFORMED;
+  account++;
+  if (NULL != (q = strchr (account,
+                           (unsigned char) '?')))
+  {
+    char *s;
+
+    s = GNUNET_strndup (account,
+                        q - account);
+    if (1 != sscanf (s,
+                     "%llu",
+                     &no))
+    {
+      GNUNET_free (s);
+      return TALER_EC_PAYTO_MALFORMED;
+    }
+    GNUNET_free (s);
+  }
+  else
+  {
+    if (1 != sscanf (account,
+                     "%llu",
+                     &no))
+      return TALER_EC_PAYTO_MALFORMED;
+  }
+  if (no > MAX_ACCOUNT_NO)
+    return TALER_EC_PAYTO_MALFORMED;
+  if (NULL != r_account)
+  {
+    r_account->hostname = GNUNET_strndup (hostname,
+                                          account - hostname);
+    r_account->no = no;
+  }
+  return TALER_EC_NONE;
+}
+
+
+/**
+ * Check if the given payto:// URL is correctly formatted.
+ *
+ * @param cls the @e cls of this struct with the plugin-specific state
+ * @param account_url an account URL
+ * @return #TALER_EC_NONE if correctly formatted
+ */
+static enum TALER_ErrorCode
+taler_bank_wire_validate (void *cls,
+                          const char *account_url)
+{
+  (void) cls;
+
+  return parse_payto (account_url,
+                      NULL);
+}
+
+
+GNUNET_NETWORK_STRUCT_BEGIN
+/**
+ * Format we used for serialized transaction data.
+ */
+struct BufFormatP
+{
+
+  /**
+   * The wire transfer identifier.
+   */
+  struct TALER_WireTransferIdentifierRawP wtid;
+
+  /**
+   * The amount.
+   */
+  struct TALER_AmountNBO amount;
+
+  /* followed by 0-terminated origin account URL */
+
+  /* followed by 0-terminated destination account URL */
+
+  /* followed by 0-terminated exchange base URL */
+
+  /* optionally followed by 0-terminated origin username URL */
+
+  /* optionally followed by 0-terminated origin password URL */
+
+};
+GNUNET_NETWORK_STRUCT_END
+
+
+/**
+ * Abort preparation of a wire transfer. For example,
+ * because we are shutting down.
+ *
+ * @param cls the @e cls of this struct with the plugin-specific state
+ * @param pth preparation to cancel
+ */
+static void
+taler_bank_prepare_wire_transfer_cancel (void *cls,
+                                         struct TALER_WIRE_PrepareHandle *pth)
+{
+  if (NULL != pth->task)
+    GNUNET_SCHEDULER_cancel (pth->task);
+  TALER_BANK_auth_free (&pth->auth);
+  GNUNET_free (pth->origin_account_url);
+  GNUNET_free (pth->destination_account_url);
+  GNUNET_free (pth->exchange_base_url);
+  GNUNET_free (pth);
+}
+
+
+/**
+ * Prepare for exeuction of a wire transfer.  Calls the
+ * callback with the serialized state.
+ *
+ * @param cls the `struct TALER_WIRE_PrepareHandle`
+ */
+static void
+do_prepare (void *cls)
+{
+  struct TALER_WIRE_PrepareHandle *pth = cls;
+  size_t len_i;
+  size_t len_o;
+  size_t len_au;
+  size_t len_ap;
+  size_t len_b;
+  struct BufFormatP bf;
+
+  pth->task = NULL;
+  /* serialize the state into a 'buf' */
+  len_o = strlen (pth->origin_account_url) + 1;
+  len_i = strlen (pth->destination_account_url) + 1;
+  len_b = strlen (pth->exchange_base_url) + 1;
+  switch (pth->auth.method)
+  {
+  case TALER_BANK_AUTH_NONE:
+    len_au = 0;
+    len_ap = 0;
+    break;
+  case TALER_BANK_AUTH_BASIC:
+    len_au = strlen (pth->auth.details.basic.username) + 1;
+    len_ap = strlen (pth->auth.details.basic.password) + 1;
+    break;
+  }
+  bf.wtid = pth->wtid;
+  TALER_amount_hton (&bf.amount,
+                     &pth->amount);
+  {
+    char buf[sizeof (struct BufFormatP) + len_o + len_i + len_b + len_au + len_ap];
+
+    memcpy (buf,
+            &bf,
+            sizeof (struct BufFormatP));
+    memcpy (&buf[sizeof (struct BufFormatP)],
+            pth->origin_account_url,
+            len_o);
+    memcpy (&buf[sizeof (struct BufFormatP) + len_o],
+            pth->destination_account_url,
+            len_i);
+    memcpy (&buf[sizeof (struct BufFormatP) + len_o + len_i],
+            pth->exchange_base_url,
+            len_b);
+    switch (pth->auth.method)
+    {
+    case TALER_BANK_AUTH_NONE:
+      break;
+    case TALER_BANK_AUTH_BASIC:
+      memcpy (&buf[sizeof (struct BufFormatP) + len_o + len_i + len_b],
+              pth->auth.details.basic.username,
+              len_au);
+      memcpy (&buf[sizeof (struct BufFormatP) + len_o + len_i + len_b + len_au],
+              pth->auth.details.basic.password,
+              len_ap);
+      break;
+    }
+    /* finally give the state back */
+    pth->ptc (pth->ptc_cls,
+              buf,
+              sizeof (buf));
+  }
+  taler_bank_prepare_wire_transfer_cancel (NULL,
+                                           pth);
+}
+
+
+/**
+ * Parse account configuration from @a cfg in @a section into @a account.
+ * Obtains the URL option and initializes @a account from it.
+ *
+ * @param cfg configuration to parse
+ * @param section section with the account configuration
+ * @param account[out] account information to initialize
+ * @return #GNUNET_OK on success
+ */
+static int
+parse_account_cfg (const struct GNUNET_CONFIGURATION_Handle *cfg,
+                   const char *section,
+                   struct Account *account)
+{
+  char *account_url;
+
+  if (GNUNET_OK !=
+      GNUNET_CONFIGURATION_get_value_string (cfg,
+                                             section,
+                                             "URL",
+                                             &account_url))
+  {
+    GNUNET_log_config_missing (GNUNET_ERROR_TYPE_ERROR,
+                               section,
+                               "URL");
+    return GNUNET_SYSERR;
+  }
+
+  if (TALER_EC_NONE !=
+      parse_payto (account_url,
+                   account))
+  {
+    GNUNET_log_config_invalid (GNUNET_ERROR_TYPE_ERROR,
+                               section,
+                               "URL",
+                               "Malformed payto:// URL for x-taler-bank method");
+    GNUNET_free (account_url);
+    return GNUNET_SYSERR;
+  }
+  GNUNET_free (account_url);
+  return GNUNET_OK;
+}
+
+
+/**
+ * Prepare for exeuction of a wire transfer.  Note that we should call
+ * @a ptc asynchronously (as that is what the API requires, because
+ * some transfer methods need it).  So while we could immediately call
+ * @a ptc, we first bundle up all the data and schedule a task to do
+ * the work.
+ *
+ * @param cls the @e cls of this struct with the plugin-specific state
+ * @param origin_account_section configuration section specifying the origin
+ *        account of the exchange to use
+ * @param destination_account_url payto:// URL identifying where to send the money
+ * @param amount amount to transfer, already rounded
+ * @param exchange_base_url base URL of this exchange
+ * @param wtid wire transfer identifier to use
+ * @param ptc function to call with the prepared data to persist
+ * @param ptc_cls closure for @a ptc
+ * @return NULL on failure
+ */
+static struct TALER_WIRE_PrepareHandle *
+taler_bank_prepare_wire_transfer (void *cls,
+                                  const char *origin_account_section,
+                                  const char *destination_account_url,
+                                  const struct TALER_Amount *amount,
+                                  const char *exchange_base_url,
+                                  const struct TALER_WireTransferIdentifierRawP *wtid,
+                                  TALER_WIRE_PrepareTransactionCallback ptc,
+                                  void *ptc_cls)
+{
+  struct TalerBankClosure *tc = cls;
+  struct TALER_WIRE_PrepareHandle *pth;
+  char *origin_account_url;
+  struct Account a_in;
+  struct Account a_out;
+
+  /* Check that payto:// URLs are valid */
+  if (TALER_EC_NONE !=
+      parse_payto (destination_account_url,
+                   &a_out))
+  {
+    GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
+                "payto://-URL `%s' is invalid!\n",
+                destination_account_url);
+    return NULL;
+  }
+  if (GNUNET_OK !=
+      GNUNET_CONFIGURATION_get_value_string (tc->cfg,
+                                             origin_account_section,
+                                             "URL",
+                                             &origin_account_url))
+  {
+    GNUNET_log_config_missing (GNUNET_ERROR_TYPE_ERROR,
+                               origin_account_section,
+                               "URL");
+    GNUNET_free (a_out.hostname);
+    return NULL;
+  }
+  if (TALER_EC_NONE !=
+      parse_payto (origin_account_url,
+                   &a_in))
+    {
+    GNUNET_log_config_invalid (GNUNET_ERROR_TYPE_ERROR,
+                               origin_account_section,
+                               "URL",
+                               "Malformed payto:// URL for x-taler-bank method");
+    GNUNET_free (origin_account_url);
+    GNUNET_free (a_out.hostname);
+    return NULL;
+  }
+
+  /* Make sure the bank is the same! */
+  if (0 != strcasecmp (a_in.hostname,
+                       a_out.hostname))
+  {
+    GNUNET_log (GNUNET_ERROR_TYPE_WARNING,
+                "x-taler-bank hostname missmatch: `%s' != `%s'\n",
+                a_in.hostname,
+                a_out.hostname);
+    GNUNET_free (a_in.hostname);
+    GNUNET_free (a_out.hostname);
+    return NULL;
+  }
+  GNUNET_free (a_in.hostname);
+  GNUNET_free (a_out.hostname);
+
+  pth = GNUNET_new (struct TALER_WIRE_PrepareHandle);
+  if (GNUNET_OK !=
+      TALER_BANK_auth_parse_cfg (tc->cfg,
+                                 origin_account_section,
+                                 &pth->auth))
+  {
+    GNUNET_free (pth);
+    return NULL;
+  }
+
+  pth->tc = tc;
+  pth->origin_account_url = origin_account_url;
+  pth->destination_account_url = GNUNET_strdup (destination_account_url);
+  pth->exchange_base_url = GNUNET_strdup (exchange_base_url);
+  pth->wtid = *wtid;
+  pth->ptc = ptc;
+  pth->ptc_cls = ptc_cls;
+  pth->amount = *amount;
+  pth->task = GNUNET_SCHEDULER_add_now (&do_prepare,
+                                        pth);
+  return pth;
+}
+
+
+/**
+ * Called with the result of submitting information about an incoming
+ * transaction to a bank.
+ *
+ * @param cls closure with the `struct TALER_WIRE_ExecuteHandle`
+ * @param http_status HTTP response code, #MHD_HTTP_OK (200) for successful status request
+ *                    0 if the bank's reply is bogus (fails to follow the protocol)
+ * @param ec error code from the bank
+ * @param serial_id unique ID of the wire transfer in the bank's records; UINT64_MAX on error
+ * @param json detailed response from the HTTPD, or NULL if reply was not JSON
+ */
+static void
+execute_cb (void *cls,
+            unsigned int http_status,
+            enum TALER_ErrorCode ec,
+            uint64_t serial_id,
+            const json_t *json)
+{
+  struct TALER_WIRE_ExecuteHandle *eh = cls;
+  json_t *reason;
+  const char *emsg;
+  char *s;
+
+  eh->aaih = NULL;
+  emsg = NULL;
+  if (NULL != json)
+  {
+    reason = json_object_get (json,
+                              "reason");
+    if (NULL != reason)
+      emsg = json_string_value (reason);
+  }
+  if (NULL != emsg)
+    GNUNET_asprintf (&s,
+                     "%u/%u (%s)",
+                     http_status,
+                     (unsigned int) ec,
+                     emsg);
+  else
+    GNUNET_asprintf (&s,
+                     "%u/%u",
+                     http_status,
+                     (unsigned int) ec);
+  eh->cc (eh->cc_cls,
+          (MHD_HTTP_OK == http_status) ? GNUNET_OK : GNUNET_SYSERR,
+          serial_id,
+          (MHD_HTTP_OK == http_status) ? NULL : s);
+  GNUNET_free (s);
+  GNUNET_free (eh);
+}
+
+
+/**
+ * Execute a wire transfer.
+ *
+ * @param cls the @e cls of this struct with the plugin-specific state
+ * @param buf buffer with the prepared execution details
+ * @param buf_size number of bytes in @a buf
+ * @param cc function to call upon success
+ * @param cc_cls closure for @a cc
+ * @return NULL on error
+ */
+static struct TALER_WIRE_ExecuteHandle *
+taler_bank_execute_wire_transfer (void *cls,
+                                  const char *buf,
+                                  size_t buf_size,
+                                  TALER_WIRE_ConfirmationCallback cc,
+                                  void *cc_cls)
+{
+  struct TalerBankClosure *tc = cls;
+  struct TALER_WIRE_ExecuteHandle *eh;
+  struct TALER_Amount amount;
+  struct Account origin_account;
+  struct Account destination_account;
+  struct BufFormatP bf;
+  const char *exchange_base_url;
+  const char *origin_account_url;
+  const char *destination_account_url;
+  struct TALER_BANK_AuthenticationData auth;
+  size_t left;
+  size_t slen;
+  char *wire_s;
+
+  if (NULL == tc->ctx)
+  {
+    GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
+                "Bank not initialized, cannot do transfers!\n");
+    return NULL; /* not initialized with configuration, cannot do transfers */
+  }
+  if ( (buf_size <= sizeof (struct BufFormatP)) ||
+       ('\0' != buf[buf_size - 1]) )
+  {
+    GNUNET_break (0);
+    return NULL;
+  }
+  memcpy (&bf,
+          buf,
+          sizeof (bf));
+  TALER_amount_ntoh (&amount,
+                     &bf.amount);
+  origin_account_url = &buf[sizeof (struct BufFormatP)];
+  left = buf_size - sizeof (struct BufFormatP);
+  slen = strlen (origin_account_url) + 1;
+  GNUNET_assert (left >= slen);
+  left -= slen;
+  if (0 == left)
+  {
+    GNUNET_break (0);
+    return NULL;
+  }
+  destination_account_url = &origin_account_url[slen];
+  slen = strlen (destination_account_url) + 1;
+  GNUNET_assert (left >= slen);
+  left -= slen;
+  if (0 == left)
+  {
+    GNUNET_break (0);
+    return NULL;
+  }
+  exchange_base_url = &destination_account_url[slen];
+  slen = strlen (exchange_base_url) + 1;
+  GNUNET_assert (left >= slen);
+  left -= slen;
+  if (0 == left)
+  {
+    auth.method = TALER_BANK_AUTH_NONE;
+  }
+  else
+  {
+    auth.details.basic.username = (char *) &exchange_base_url[slen];
+    slen = strlen (auth.details.basic.username) + 1;
+    GNUNET_assert (left >= slen);
+    left -= slen;
+    if (0 == left)
+    {
+      GNUNET_break (0);
+      return NULL;
+    }
+    auth.details.basic.password = &auth.details.basic.username[slen];
+    slen = strlen (auth.details.basic.username) + 1;
+    GNUNET_assert (left >= slen);
+    left -= slen;
+    if (0 != left)
+    {
+      GNUNET_break (0);
+      return NULL;
+    }
+  }
+
+  if (TALER_EC_NONE !=
+      parse_payto (origin_account_url,
+                   &origin_account))
+  {
+    GNUNET_break (0);
+    return NULL;
+  }
+  if (TALER_EC_NONE !=
+      parse_payto (destination_account_url,
+                   &destination_account))
+  {
+    GNUNET_break (0);
+    return NULL;
+  }
+  if (0 != strcasecmp (origin_account.hostname,
+                       destination_account.hostname))
+  {
+    GNUNET_break (0);
+    return NULL;
+  }
+
+  eh = GNUNET_new (struct TALER_WIRE_ExecuteHandle);
+  eh->cc = cc;
+  eh->cc_cls = cc_cls;
+  wire_s = GNUNET_STRINGS_data_to_string_alloc (&bf.wtid,
+                                                sizeof (bf.wtid));
+  eh->aaih = TALER_BANK_admin_add_incoming (tc->ctx,
+                                            origin_account.hostname,
+                                            &auth,
+                                            exchange_base_url,
+                                            wire_s,
+                                            &amount,
+                                            (uint64_t) origin_account.no,
+					    (uint64_t) destination_account.no,
+                                            &execute_cb,
+                                            eh);
+  GNUNET_free (wire_s);
+  if (NULL == eh->aaih)
+  {
+    GNUNET_break (0);
+    GNUNET_free (eh);
+    return NULL;
+  }
+  return eh;
+}
+
+
+/**
+ * Abort execution of a wire transfer. For example, because we are
+ * shutting down.  Note that if an execution is aborted, it may or
+ * may not still succeed. The caller MUST run @e
+ * execute_wire_transfer again for the same request as soon as
+ * possilbe, to ensure that the request either ultimately succeeds
+ * or ultimately fails. Until this has been done, the transaction is
+ * in limbo (i.e. may or may not have been committed).
+ *
+ * @param cls the @e cls of this struct with the plugin-specific state
+ * @param eh execution to cancel
+ */
+static void
+taler_bank_execute_wire_transfer_cancel (void *cls,
+                                         struct TALER_WIRE_ExecuteHandle *eh)
+{
+  TALER_BANK_admin_add_incoming_cancel (eh->aaih);
+  GNUNET_free (eh);
+}
+
+
+/**
+ * Handle for a #taler_bank_get_history() request.
+ */
+struct TALER_WIRE_HistoryHandle
+{
+
+  /**
+   * Function to call with results.
+   */
+  TALER_WIRE_HistoryResultCallback hres_cb;
+
+  /**
+   * Closure for @e hres_cb.
+   */
+  void *hres_cb_cls;
+
+  /**
+   * Request to the bank.
+   */
+  struct TALER_BANK_HistoryHandle *hh;
+
+  /**
+   * Authentication to use for access.
+   */
+  struct TALER_BANK_AuthenticationData auth;
+
+};
+
+
+/**
+ * Cancel going over the account's history.
+ *
+ * @param cls the @e cls of this struct with the plugin-specific state
+ * @param whh operation to cancel
+ */
+static void
+taler_bank_get_history_cancel (void *cls,
+                               struct TALER_WIRE_HistoryHandle *whh)
+{
+  if (NULL != whh->hh)
+  {
+    TALER_BANK_history_cancel (whh->hh);
+    whh->hh = NULL;
+  }
+  TALER_BANK_auth_free (&whh->auth);
+  GNUNET_free (whh);
+}
+
+
+/**
+ * Function called with results from the bank about the transaction history.
+ *
+ * @param cls the `struct TALER_WIRE_HistoryHandle`
+ * @param http_status HTTP response code, #MHD_HTTP_OK (200) for successful status request
+ *                    0 if the bank's reply is bogus (fails to follow the protocol),
+ *                    #MHD_HTTP_NO_CONTENT if there are no more results; on success the
+ *                    last callback is always of this status (even if `abs(num_results)` were
+ *                    already returned).
+ * @param ec taler error code
+ * @param dir direction of the transfer
+ * @param serial_id monotonically increasing counter corresponding to the transaction
+ * @param details details about the wire transfer
+ * @param json detailed response from the HTTPD, or NULL if reply was not in JSON
+ */
+static void
+bhist_cb (void *cls,
+          unsigned int http_status,
+          enum TALER_ErrorCode ec,
+          enum TALER_BANK_Direction dir,
+          uint64_t serial_id,
+          const struct TALER_BANK_TransferDetails *details,
+          const json_t *json)
+{
+  struct TALER_WIRE_HistoryHandle *whh = cls;
+  uint64_t bserial_id = GNUNET_htonll (serial_id);
+  struct TALER_WIRE_TransferDetails wd;
+
+  switch (http_status) {
+  case MHD_HTTP_OK:
+    {
+      char *subject;
+      char *space;
+
+      wd.amount = details->amount;
+      wd.execution_date = details->execution_date;
+      subject = GNUNET_strdup (details->wire_transfer_subject);
+      space = strchr (subject,
+                      (unsigned char) ' ');
+      if (NULL != space)
+      {
+        /* Space separates the actual wire transfer subject from the
+           exchange base URL (if present, expected only for outgoing
+           transactions).  So we cut the string off at the space. */
+        *space = '\0';
+      }
+      /* NOTE: For a real bank, the subject should include a checksum! */
+      if (GNUNET_OK !=
+          GNUNET_STRINGS_string_to_data (subject,
+                                         strlen (subject),
+                                         &wd.wtid,
+                                         sizeof (wd.wtid)))
+      {
+        /* Ill-formed wire subject, set binary version to all zeros
+           and pass as a string, this time including the part after
+           the space. */
+        memset (&wd.wtid,
+                0,
+                sizeof (wd.wtid));
+        wd.wtid_s = details->wire_transfer_subject;
+      }
+      else
+      {
+        wd.wtid_s = NULL;
+      }
+      GNUNET_free (subject);
+      wd.account_url = details->account_url;
+      if ( (NULL != whh->hres_cb) &&
+           (GNUNET_OK !=
+            whh->hres_cb (whh->hres_cb_cls,
+                          TALER_EC_NONE,
+                          dir,
+                          &bserial_id,
+                          sizeof (bserial_id),
+                          &wd)) )
+        whh->hres_cb = NULL;
+      return; /* do NOT yet clean up! */
+    }
+  case MHD_HTTP_NO_CONTENT:
+    if (NULL != whh->hres_cb)
+      (void) whh->hres_cb (whh->hres_cb_cls,
+                           ec,
+                           TALER_BANK_DIRECTION_NONE,
+                           NULL,
+                           0,
+                           NULL);
+    break;
+  default:
+    GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
+                "Bank failed with HTTP status %u (EC: %u)\n",
+                http_status,
+                ec);
+    if (NULL != whh->hres_cb)
+      (void) whh->hres_cb (whh->hres_cb_cls,
+                           ec,
+                           TALER_BANK_DIRECTION_NONE,
+                           NULL,
+                           0,
+                           NULL);
+    break;
+  }
+  whh->hh = NULL;
+  taler_bank_get_history_cancel (NULL,
+                                 whh);
+}
+
+
+/**
+ * Query transfer history of an account.  We use the variable-size
+ * @a start_off to indicate which transfers we are interested in as
+ * different banking systems may have different ways to identify
+ * transfers.  The @a start_off value must thus match the value of
+ * a `row_off` argument previously given to the @a hres_cb.  Use
+ * NULL to query transfers from the beginning of time (with
+ * positive @a num_results) or from the lataler_bank committed transfers
+ * (with negative @a num_results).
+ *
+ * @param cls the @e cls of this struct with the plugin-specific state
+ * @param account_section specifies the configuration section which
+ *        identifies the account for which we should get the history
+ * @param direction what kinds of wire transfers should be returned
+ * @param start_off from which row on do we want to get results, use NULL for the lataler_bank; exclusive
+ * @param start_off_len number of bytes in @a start_off; must be `sizeof(uint64_t)`.
+ * @param num_results how many results do we want; negative numbers to go into the past,
+ *                    positive numbers to go into the future starting at @a start_row;
+ *                    must not be zero.
+ * @param hres_cb the callback to call with the transaction history
+ * @param hres_cb_cls closure for the above callback
+ */
+static struct TALER_WIRE_HistoryHandle *
+taler_bank_get_history (void *cls,
+                        const char *account_section,
+                        enum TALER_BANK_Direction direction,
+                        const void *start_off,
+                        size_t start_off_len,
+                        int64_t num_results,
+                        TALER_WIRE_HistoryResultCallback hres_cb,
+                        void *hres_cb_cls)
+{
+  struct TalerBankClosure *tc = cls;
+  struct TALER_WIRE_HistoryHandle *whh;
+  const uint64_t *start_off_b64;
+  uint64_t start_row;
+  struct Account account;
+
+  if (0 == num_results)
+  {
+    GNUNET_break (0);
+    return NULL;
+  }
+  if (TALER_BANK_DIRECTION_NONE == direction)
+  {
+    GNUNET_break (0);
+    return NULL;
+  }
+  if ( (NULL != start_off) &&
+       (sizeof (uint64_t) != start_off_len) )
+  {
+    GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
+                "Wire plugin 'taler_bank' got start offset of wrong size (%llu instead of %llu)\n",
+                (unsigned long long) start_off_len,
+                (unsigned long long) sizeof (uint64_t));
+    GNUNET_break (0);
+    /* Probably something is wrong with the DB, some other component
+     * wrote a wrong value to it.  Instead of completely stopping to work,
+     * we just scan from the beginning. */
+    start_off = NULL;
+  }
+  if (NULL == start_off)
+  {
+    start_row = UINT64_MAX; /* no start row */
+  }
+  else
+  {
+    start_off_b64 = start_off;
+    start_row = GNUNET_ntohll (*start_off_b64);
+  }
+  if (GNUNET_OK !=
+      parse_account_cfg (tc->cfg,
+                         account_section,
+                         &account))
+    return NULL;
+
+  whh = GNUNET_new (struct TALER_WIRE_HistoryHandle);
+  if (GNUNET_OK !=
+      TALER_BANK_auth_parse_cfg (tc->cfg,
+                                 account_section,
+                                 &whh->auth))
+  {
+    GNUNET_free (whh);
+    return NULL;
+  }
+
+  whh->hres_cb = hres_cb;
+  whh->hres_cb_cls = hres_cb_cls;
+  whh->hh = TALER_BANK_history (tc->ctx,
+                                account.hostname,
+                                &whh->auth,
+                                (uint64_t) account.no,
+                                direction,
+                                start_row,
+                                num_results,
+                                &bhist_cb,
+                                whh);
+  if (NULL == whh->hh)
+  {
+    GNUNET_break (0);
+    taler_bank_get_history_cancel (NULL,
+                                   whh);
+    GNUNET_free (account.hostname);
+    return NULL;
+  }
+  GNUNET_free (account.hostname);
+  return whh;
+}
+
+
+/**
+ * Context for a rejection operation.
+ */
+struct TALER_WIRE_RejectHandle
+{
+  /**
+   * Function to call with the result.
+   */
+  TALER_WIRE_RejectTransferCallback rej_cb;
+
+  /**
+   * Closure for @e rej_cb.
+   */
+  void *rej_cb_cls;
+
+  /**
+   * Handle for the reject operation.
+   */
+  struct TALER_BANK_RejectHandle *brh;
+
+  /**
+   * Authentication information to use.
+   */
+  struct TALER_BANK_AuthenticationData auth;
+};
+
+
+/**
+ * Callbacks of this type are used to serve the result of asking
+ * the bank to reject an incoming wire transfer.
+ *
+ * @param cls closure
+ * @param http_status HTTP response code, #MHD_HTTP_NO_CONTENT (204) for successful status request;
+ *                    #MHD_HTTP_NOT_FOUND if the rowid is unknown;
+ *                    0 if the bank's reply is bogus (fails to follow the protocol),
+ * @param ec detailed error code
+ */
+static void
+reject_cb (void *cls,
+           unsigned int http_status,
+           enum TALER_ErrorCode ec)
+{
+  struct TALER_WIRE_RejectHandle *rh = cls;
+
+  rh->brh = NULL;
+  rh->rej_cb (rh->rej_cb_cls,
+              ec);
+  GNUNET_free (rh);
+}
+
+
+/**
+ * Cancel ongoing reject operation.  Note that the rejection may still
+ * proceed. Basically, if this function is called, the rejection may
+ * have happened or not.  This function is usually used during shutdown
+ * or system upgrades.  At a later point, the application must call
+ * @e reject_transfer again for this wire transfer, unless the
+ * @e get_history shows that the wire transfer no longer exists.
+ *
+ * @param cls plugins' closure
+ * @param rh operation to cancel
+ * @return closure of the callback of the operation
+ */
+static void *
+taler_bank_reject_transfer_cancel (void *cls,
+                                   struct TALER_WIRE_RejectHandle *rh)
+{
+  void *ret = rh->rej_cb_cls;
+
+  if (NULL != rh->brh)
+    TALER_BANK_reject_cancel (rh->brh);
+  TALER_BANK_auth_free (&rh->auth);
+  GNUNET_free (rh);
+  return ret;
+}
+
+
+/**
+ * Reject an incoming wire transfer that was obtained from the
+ * history. This function can be used to transfer funds back to
+ * the sender if the WTID was malformed (i.e. due to a typo).
+ *
+ * Calling `reject_transfer` twice on the same wire transfer should
+ * be idempotent, i.e. not cause the funds to be wired back twice.
+ * Furthermore, the transfer should henceforth be removed from the
+ * results returned by @e get_history.
+ *
+ * @param cls plugin's closure
+ * @param account_section specifies the configuration section which
+ *        identifies the account to use to reject the transfer
+ * @param start_off offset of the wire transfer in plugin-specific format
+ * @param start_off_len number of bytes in @a start_off
+ * @param rej_cb function to call with the result of the operation
+ * @param rej_cb_cls closure for @a rej_cb
+ * @return handle to cancel the operation
+ */
+static struct TALER_WIRE_RejectHandle *
+taler_bank_reject_transfer (void *cls,
+                            const char *account_section,
+                            const void *start_off,
+                            size_t start_off_len,
+                            TALER_WIRE_RejectTransferCallback rej_cb,
+                            void *rej_cb_cls)
+{
+  struct TalerBankClosure *tc = cls;
+  const uint64_t *rowid_b64 = start_off;
+  struct TALER_WIRE_RejectHandle *rh;
+  struct Account account;
+
+  if (sizeof (uint64_t) != start_off_len)
+  {
+    GNUNET_break (0);
+    return NULL;
+  }
+  rh = GNUNET_new (struct TALER_WIRE_RejectHandle);
+  if (GNUNET_OK !=
+      TALER_BANK_auth_parse_cfg (tc->cfg,
+                                 account_section,
+                                 &rh->auth))
+  {
+    GNUNET_free (rh);
+    return NULL;
+  }
+  if (GNUNET_OK !=
+      parse_account_cfg (tc->cfg,
+                         account_section,
+                         &account))
+  {
+    (void) taler_bank_reject_transfer_cancel (tc,
+                                              rh);
+    return NULL;
+  }
+  rh->rej_cb = rej_cb;
+  rh->rej_cb_cls = rej_cb_cls;
+  rh->brh = TALER_BANK_reject (tc->ctx,
+                               account.hostname,
+                               &rh->auth,
+                               (uint64_t) account.no,
+                               GNUNET_ntohll (*rowid_b64),
+                               &reject_cb,
+                               rh);
+  if (NULL == rh->brh)
+  {
+    (void) taler_bank_reject_transfer_cancel (tc,
+                                              rh);
+    GNUNET_free (account.hostname);
+    return NULL;
+  }
+  GNUNET_free (account.hostname);
+  return rh;
+}
+
+
+/**
+ * Initialize taler_bank-wire subsystem.
+ *
+ * @param cls a configuration instance
+ * @return NULL on error, otherwise a `struct TALER_WIRE_Plugin`
+ */
+void *
+libtaler_plugin_wire_taler_bank_init (void *cls)
+{
+  struct GNUNET_CONFIGURATION_Handle *cfg = cls;
+  struct TalerBankClosure *tc;
+  struct TALER_WIRE_Plugin *plugin;
+
+  tc = GNUNET_new (struct TalerBankClosure);
+  tc->cfg = cfg;
+  if (GNUNET_OK !=
+      GNUNET_CONFIGURATION_get_value_string (cfg,
+                                             "taler",
+                                             "CURRENCY",
+                                             &tc->currency))
+  {
+    GNUNET_log_config_missing (GNUNET_ERROR_TYPE_ERROR,
+                               "taler",
+                               "CURRENCY");
+    GNUNET_free (tc);
+    return NULL;
+  }
+  tc->ctx = GNUNET_CURL_init (&GNUNET_CURL_gnunet_scheduler_reschedule,
+                              &tc->rc);
+  tc->rc = GNUNET_CURL_gnunet_rc_create (tc->ctx);
+  if (NULL == tc->ctx)
+  {
+    GNUNET_break (0);
+    GNUNET_free (tc->currency);
+    GNUNET_free (tc);
+    return NULL;
+  }
+  plugin = GNUNET_new (struct TALER_WIRE_Plugin);
+  plugin->cls = tc;
+  plugin->method = "x-taler-bank";
+  plugin->amount_round = &taler_bank_amount_round;
+  plugin->wire_validate = &taler_bank_wire_validate;
+  plugin->prepare_wire_transfer = &taler_bank_prepare_wire_transfer;
+  plugin->prepare_wire_transfer_cancel = &taler_bank_prepare_wire_transfer_cancel;
+  plugin->execute_wire_transfer = &taler_bank_execute_wire_transfer;
+  plugin->execute_wire_transfer_cancel = &taler_bank_execute_wire_transfer_cancel;
+  plugin->get_history = &taler_bank_get_history;
+  plugin->get_history_cancel = &taler_bank_get_history_cancel;
+  plugin->reject_transfer = &taler_bank_reject_transfer;
+  plugin->reject_transfer_cancel = &taler_bank_reject_transfer_cancel;
+  return plugin;
+}
+
+
+/**
+ * Shutdown taler-bank wire subsystem.
+ *
+ * @param cls a `struct TALER_WIRE_Plugin`
+ * @return NULL (always)
+ */
+void *
+libtaler_plugin_wire_taler_bank_done (void *cls)
+{
+  struct TALER_WIRE_Plugin *plugin = cls;
+  struct TalerBankClosure *tc = plugin->cls;
+
+  if (NULL != tc->ctx)
+  {
+    GNUNET_CURL_fini (tc->ctx);
+    tc->ctx = NULL;
+  }
+  if (NULL != tc->rc)
+  {
+    GNUNET_CURL_gnunet_rc_destroy (tc->rc);
+    tc->rc = NULL;
+  }
+  GNUNET_free_non_null (tc->currency);
+  GNUNET_free (tc);
+  GNUNET_free (plugin);
+  return NULL;
+}
+
+/* end of plugin_wire_taler-bank.c */